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- Move order of menu header items (e.g. back button and daily toggle) so
  that they follow the submenu nav buttons using keyboard navigation.
- Support selection on SPACE for color/background tiles.
- Like backgrounds/colors, use arrowkeys instead of TAB to navigate the
  shortcut options (i.e. TAB to focus the shortcuts menu, then use
  arrowkeys to move between the shortcut options).
- Add role=button to upload & default background tiles for screenreader
  support.

Bug: 953822
Change-Id: Iae8c1b8390d917f1513e234b46f0b75cc9bae3ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1737743
Commit-Queue: Kristi Park <kristipark@chromium.org>
Reviewed-by: Gayane Petrosyan <gayane@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684407}